The lower jaw (mandible) is supported for movement relative to the upper jaw (maxilla) by a pair of temporomandibular joints which interconnect the lower jaw and skull in front of the ears on each side of the head. The temporomandibular joints determine the particular range of motion of the lower jaw and its positional relationship to the upper jaw. Protrusion and lateral excursion of the lower jaw varies from person to person.
In performing reconstructive dentistry, such as fitting a person with full or partial dentures, the particular range of motion of a patient's lower jaw must be taken into account to provide proper clearance for chewing as well as for opening and closing of the mouth without grinding or other unnecessary interference between the teeth. This procedure usually entails taking various measurements of the mandibular motion and then transferring these measurements to a dental articulator like that shown in U.S. Pat. No. 3,624,906 to Granger for reproducing the movements to facilitate adjustment and fitting of the appliances to the patient. Measurement of mandibular motion also can be useful in diagnosing or treating problems associated with the temporomandibular joints.
The mandibular motion recorders of the prior art, however, have not been altogether satisfactory. Some of the prior devices have not been interchangeable between patients having either dentulous (with teeth) or edentulous (without teeth) mouths, or have been interchangeable only with the addition of elaborate accessories. Some devices have not operated completely smoothly but have tended to catch or bind in portions of the movement. Such binding or roughness in action reduces accuracy of the measurement and causes some discomfort to the patient. In addition, the prior devices for recording mandibular motion have tended to be cumbersome and difficult to manipulate, and have suffered from the further disadvantages of undue complexity in construction and therefore expense.
A need has thus arisen for a new and improved apparatus for recording mandibular motion.